Metal alloy



Patented Apr. 28, 1953 UNITED STATES PATENT OFFICE METAL ALLOY SidneyLow, Springfield, Mass.

No Drawing. Application January 3, 1951, Serial No. 204,261"

1 Claim.

. The principal objects of. the invention -aredi-' rected to theprovision of an alloy which has greater qualities of castability inplaster of Paris than known prior art alloys which has a high resistanceto corrosion, and which has a low melting point.

The novel features of my invention are attained by the new and uniquecombination of certain specific elements in predetermined proportions,the elements themselves beingselected for their individualcharacteristics and for their ability to combine with other elements soas to produce an end result possessing properties for the casting ofdentures superior to any known prior art alloys. e

A prime requisite in alloys of the type herein referred to iscastability. It must form aliquid of low viscosity when heated to thecasting temperature so as to permit an easy and rapid flow into themold.

A minimum amount of heat between the melting point and the castingtemperatureis a desideratum. With such minimum attained, oxidation isminimized and the chances for interaction with the mold surfaces arelikewise lessened.

Such objectives are easily attained by means of the alloy of myinvention. That is to say, the alloy is adapted to form castings whichare homogeneous, dense, and free from pits r blowholes.

Another requisite in alloys of this type is a freedom from change instrength or hardness upon cooling. Shrinkage must be negligible forobvious reasons. The degree of corrosion resistance must be high, alsofor obvious reasons.

Other objects and advantages of my invention will be readily apparent byreference to the following specification and it is to be understood thatany modifications may be made in the exact details herein described,within the scope of the appended claim, without departing from orexceeding the spirit of the invention.

, The alloy described and explained herein is to be considered asconsisting of a plurality of elements namely carbon, manganese, silicon,chromium, molybdenum, nickel, cobalt, colurnbium, copper, aluminum, andiron.

As to the various elements employed in my invention, I deem it importantto explain why each is used.

Carbon Manganese serves as a deoxidizer.

It Serves as an aid to the melting of the alloy.

Furthermore, it is used to clean up a melt prior to tapping.

It increases the fluidity of the alloy permitting lighter sections to becast successfully.

Silicon serves as an aid to the melting of the alloy. As with manganese,it is also used to clean up a melt prior to tapping. That is to say, ithelps to reduce the surface film. Too, it increases the corrosionresistance of the alloy since it is a powerful deoxidizer. It alsoserves to increase the fluidity of the alloy.

Chromium Chromium imparts strength and hardness to the alloy and'servesto increase its corrosion resistance.

Molybdenum The molybdenum-serves to increase corrosion resistance inreducing media such as is so frequently encountered in the human mouth.It also increases the elevated temperature strength of the alloy,thereby minimizing hot cracks.

Tungsten is interchangeable with molybdenum, and like molybdenum, servesto increase corrosion resistance in reducing media. It also increasesthe elevated temperature strength, minimizing hot tearing.

Nickel Nickel serves as a very excellent base to which thealloy-ingadditions may be made.

It possesses fair corrosion resistance properties and it has areasonably low melting point.

It will be observed that the other alloying additions may be added tothe nickel base since all are readily soluble. in both molten and solidnickel.

Nickel imparts toughness and ductility to the alloy.

Cobalt Columbz'um I Columbi-um is not employed only as a carbidestabilizer. Inmy alloy, it also serves to increase resistance to hottearingand to increase fluidity by altering the copper-aluminum richoxide film which forms during the melting.

Columbium gives sufiicient fluidity to run in the thin areas of thedental castings such as saddles.

It is an all important alloy addition without which the requisitefluidity would not be obtained.

Tantalum Tantalum is interchangeable with columbium, and, likecolumbium, serves as a carbide stabilizer. In my alloy, it serves toincrease resistance to hot tearing and to increase fluidity by alteringthe copper-aluminum rich oxide film which forms during the melting.Whenever tantalum is referred to in this specification, it will beunderstood that it may be used interchangeably with columbium.

With columbium and/or tantalum, sections as thin as 0.008" can be run.Sections thinner than 0.025" cannot be run without columbium and/ortantalum. The average dental casting has sections as thin as 0.010".

Copper Copper serves to aid in the forming of the protective skin in themolten alloy which permits same to be cast in plaster of Paris boundinvestments. If this skin is not formed, the alloy reacts vigorouslywith the sulphur in the investment and is valueless. Copper reduces themelting point of the alloy.

Aluminum Aluminum together with copper serves to form the protectiveskin in the molten alloy.

The copper and aluminum must be added in the proper ratio in order toobtain this protective skin.

I have found that the combination of aluminum and copper permits highercopper additions to be made without the precipitation of free copper.

The copper and aluminum must be added in the form of a master alloy as Ihave found that additions of metallic copper and aluminum will notresult in the desired alloy,

What is all important in my invention is not the indiscriminate additionof aluminum but the maintenance of the all important copper aluminumratio.

Iron

A minimum of iron is desired as it reacts unfavorably with any sulphurpresent in the investment in which the alloy is castand it further tendsto raise the melting point.

Further, it is desirable to keep its amount to a minimum so as to attainas high a degree of corrosion resistance as possible.

Following is a table giving the elements that go to make up the alloy:

It will be appreciated that this table ives minimum and maximumpercentages by weight or each element.

The absolute minimum of each element is to be avoided except, of course,in the case of iron.

The ranges of carbon, manganese, silicon, chromium, molybdenum, nickel,cobalt, columbium, copper, aluminum, and iron have been coordinated witheach other nly as a result of considerable experimentation on my part.

The minimum claimed amounts of the elements have not been arbitrarilyselected and, in each instance, same has been established only as aresult of my experimentation.

As to the criticalness of the proportions, I have determined, afterconsiderable experimentation as follows:

Carbon (C) Carbon in quantities less than 0.05% is primarily animpurity. Within the range 0.05%- 0.15%, carbon increases in strength ata slight decrease in ductility and corrosion resistance. For certaindental, surgical, and jewelry applications, it is sometimes desirable totake advantage of the strengthening efiect of an increase in the carboncontent to Within the range 0.15 2.0%. I have found, however, that whenthe carbon content exceeds 2.0% the alloy becomes objectionably brittle.The hardness is increased whereas the ductility and corrosion resistanceis decreased.

The physical properties of the alloy containing within the range of0.05%-0.15% of carbon have been found to Le suited ideally for mostdental applications.

Manganese (Mn) As the manganese is increased in quantity, the fluidityof the alloy is proportionately increased, within certain limits.

I have found that the best results are obtained when manganese is usedWithin the range 0.70%- 0.90%.

If maximum fluidity is desired, the manganese content may be raised toas much as 2.0%. Under no conditions, however, should the manganesecontent exceed 2.0% since the resultant alloy is then subject to hottearing.

Silicon (Si) I have found that at least as a very minimum 1.0% isrequired for adequate fluidity and that at the very most a maximum of3.0% must not be exceeded. To exceed 3.0% will produce an objectionablybrittle alloy.

Chromium (Cr) A minimum of 10.0% is required to insure adequatecorrosion resistance in the human mouth. When the content is less than10.0%, the resultant product is not corrosion resistant and a maximum ofany more than 30.0% must not be exceeded or the meltin point of thealloy will be too high and the ductility will be too low. Furthermore,if the content is more than 30.0%, the chromium will combine with thesulphur in the plaster of Paris investments, and will tend to harden thealloy and to render it less ductile.

I have found from experiment that chromium contents greater than 20.0%make the alloy coarse grained and brittle,

I have found that chromium within a range of 17.5%-19.5% is ideal foradequate corrosion resistance with a reasonable safety factor.

If the carbon content is greater than 0.l 5%,

5, the chromium content must be accordingly increased in order tocompensate for. that portion of the chromium which combines with thecarbon so as to render itself unavailable for corrosion resistancefunctions.

Molybdenum (MID) A. minimum of 3.0% is required in order to obtaindesired effects relative to resistance to pitting, corrosion, increase,in hot strength.

I have also found that a content of molybdenum amounting to more than12.0% will result in an alloy which is objectionably brittle.

' A content within the range 9.0'%.10.0% insures that even the mostdelicate of dental castings will be cracl: free,

Nickel (Ni) Nickel serves as one of the bases in which the otherelements are soluble in the liquid and solid states.

' Cobalt At least 20.0% of cobalt must be used in order to insurefreedom from hot tearing.

. Because cobalt costs roughly 400% more than niclzehit is obviouslydesirable to maintain the cobalt content as low as possible.

1 The preferred range is within 23.0%25.0%.

Colombians (Cb) Columbium serves to increase the corrosion resistance asa carbide stabilizer and also to increase fluidity.

I have found that 0.40% as a minimum must be used in order to obtain thedesired effect. A

maximum of 2.0% must not be exceeded or the alloy willbecorne toobrittle,

In lieuof columbium, tantalum may be used with equally effectiveresults.

Copper (Cu) In my alloy, I provide a minimum of 5.0% copper.

If the pouring temperature at the alloy is high, optimum results areobtained when the copper content is 10.0%.

I do not exceed a maximum of 20.0% as I have found that an excessiveamount makes the alloy brittle.

Other alloys in the art employ a maximum of 10.0% of copper. In suchprior art disclosures, the coppercontent is held below 10.0% in order toprevent tree copper from being thrown out from the solution when itsolidifies.

Aluminum (Al) Likewise, in my alloy, I provide a minimum of 0.6% ofaluminum in order to obtain the desired result. If the pouringtemperature of the alloy is high, best results are obtained when thealuminum content is 0.8%.

Other alloys in the art known to me employ no aluminum.

I have found that the aluminum content should never exceed 2.0%. if usedin any greater quailtity, the alloy is embrittled and rendered subjectto hot tearing.

Optimum results are obtained when the copperaluminum ratio is 8-12z1.This is all important in my invention. The addition of copper andaluminum may not be indiscriminate. The ratio is the important factor.

Iron (Fe) Iron is an impurity not intentionally added,

I have found that the iron content should not exceed 10.0% or the alloyis subject to hot tearing and loses much of its ductility and corrosionresistance.

Particularly desirable results have been obtained where the proportionsare as follows:

Per cent Carbon 0.05 Manganese 0.70 Silicon 1.20 Chromium 17.5Molybdenum 9.0 Nickel 29.0 Cobalt 23.0 Columbium 0.6 Copper 10.0Aluminum 0.8 Iron Balance The alloy is high in copper and aluminum andhas very marked resistance to the action of sulphur which is present inthe usual investments in which castings are made. Plaster of Paris is anordinary material used for investments.

Also, the alloy is very low in iron which is necessary to overcomecorrosion and hold the melting point below a range where expensive andcomplicated equipment must be used.

Castings made from the alloy when taken from the mold have a pleasinglybright and clean ap-. pearance, are ductile, and possess goodmachineability.

The combination of elements provide a casting, having an outer layer orskin which is rich in copper and aluminum, which is desired for itsresistance to sulphur attack in the mold. This skin is only a fewmillionths of an inch thick and is subsequently polished off.

Were manganese not used in my alloy, the alloy would be wild when meltedin the oasting machine crucible. The correct proportion of manganese asset forth above is critical to my resultant product.

If silicon was not added to my alloy, same would lacl: fluidity andwould be wild when melted in the casting machine crucible. Silicon is acritical element in my alloy.

Were chromium not added to my alloy in the production thereof, the alloywould corrode rapidly in the human mouth, both in the areas exposed tothe air and in those areas in close contact with tissue or with teeth.Chromium is a critical element in my alloy.

If molybdenum was not added thereto, the

alloy would pit in areas in close contact with the tissue or the teeth.The hot strength of the alloy would be too low to permit obtaining a hottear-free casting in a plaster of Paris bound investment. The correctproportion of molybdenum as set forth herein is critical to my resultingalloy.

If cobalt was not incorporated as a part of my alloy, same would tearbadly When cast in plaster of Paris bound investments. It a criticalelement in my alloy.

Columbium is acritical element in the sense that were it not used, thealloy would lack fluidity and would be subject to hot tearing.

Copper is critical since were it not added, and in the proper quantity,it would not be possible to cast the alloy in plaster of Paris boundin-- vestments due to the sulphur reaction.

. Aluminum is likewise critical and for the same reason as given forcopper, namely, that were it 7. not added, the alloy'could not be castin plaster of Paris bound investments.

It should be added here that neither copper nor aluminum is effectivewhen used alone and the ratio of copper and aluminum as set forth abovemustbe maintained. It is this ratio which is all important. The elementsin the specific proportions above set forth provide an alloy, which hasa low melting': point of about 2300 F. to facilitate ready and easycasting in ordinaryinvestments, presents. a brilliant appearance, hasmarked resistance to corrosion, and possesses a very desirable ductilityand machinability.

The base composition used for producing the alloycomprises:

Per cent Carbon,;; 0.05-0.15 Manganese 0.80- 1.0 Silicon 1.40-1.60Shromium 20.5-22.5 Molybdenum 10.0-11.0 Nickel 30.0-32.0 Cobalt24.0-26.0 Columbium 0.7- 0.8 Iron approx. 4.0

' The as cast" tensile properties of this base composition are asfollows:

Tensile strength, 100,000-120,000 p. s. i. Yield"strength, 70,000-90,000p. s. i. Elongation, 1015 per cent Reduction of. area, 25-35 per centHardness, Rockwell C"-18-25 The copper and aluminum must be added in theform of a master alloy addition of the following composition:

, Per cent.

Aluminum 6.0-12.0 Iron 0.6- 2.0 Copper Balance The hardness and strengthmay also be further increased by the addition of more aluminum either byitself or in the form of a master al loy such as nickel-aluminum.

- The control of hardness and strength may also be effected by the useof a so-called hardener melt having nominally the same composition asthe base melt except that the aluminum and copper are added separately.Suitable combinations of hardener and base" melts may then be made toprocure any desired hardness.

The numerical amounts of the claimed ranges of the elements of my alloyinvolve more than a mere departure from the disclosures of the prior artwhich are known to me and effort is made herein to set forth thepatentable differences.

For example, I am aware of a prior art alloy which employs proportionsof elements as follows: it W Per cent Carbon between 0.1 and 1.0Manganese between 0.1 and 1.0 Silicon between 0.2 and 1.0 Chromiumbetween 18.0 and 28.0 Molybdenum between 4.0 and 12.0 Nickel between19.0 and 40.0 Cobalt between 18.0 and 40.0 Copper between 1.0 and 10.0Columbium and aluminum are not used in this alloy.

The normal investment used in work of the type contemplated with thisand similar alloys is a plaster of Paris bound silica investment. Thevalue of the alloy of this prior art disclosure is minimized due to thesulphur reaction. This alloy is not castable due to this objectionablesulphur reaction. Since the alloy contains copper alone, the copper doesnot prevent the sulphur reaction, even if and when the alloy is madewith the maximum of copper, namely 10%.

Also, I am aware of another prior art alloy which employs otherproportions of elements. This alloy comprises 63 parts nickel, 5 partscopper, 15 parts chromium, 10 parts molybdenum chromium alloy in equalpercentages, 2 parts tungsten, 1 parts aluminum, 1 partsmanganese-titanium alloy (70 parts manganese and 30 parts titanium), 1part manganese-boron alloy (70 parts manganese and 30 parts boron), 1part copper-silicon alloy parts copper and 20 parts silicon) and /2 partboron suboxid.

In this alloy the chromium content may be varied between 15.0 and 21.0%.The nickel may be varied between 55.0 and 65.0%, the copper may bevaried between 5.0 and 11.0%, and the aluminum may be varied between 0.5and 1.5%.

Cobalt and columbium are not even used in this alloy.

Taking this disclosure to the top side of the chemistry where thequantities of copper and aluminum are the highest, the desiredcastability might be obtained but the alloy would lack the all-importantquality of fluidity. The alloy lacks suificient silicon to increase thefluidity and is subject to the most severe form of hot tearing due tothe insuflicient hot strength.

The use or" titanium in this alloy seriously alters the oxide film,reduces the fluidity, reduces the hot strength, and increases the rateof the sulphur reaction.

The use of boron in this alloy rapidly accelerates the sulphur reactionwhich I avoid in my alloy and reduces the hot strength markedly.

In neither of the above referred to alloys is columbium and/or tantalumused.

While there are several cobalt and nickel base alloys available thatcounteract the faults of the cast gold dental alloys, they too haveserious drawbacks, viz. (1) high melting points necessitate costlymelting equipment; (2) high melting points coupled with low resistanceto sulphur attack prohibit the use of the plaster of Paris (calciumsulphate) type of investments. The more complex investments requiredzirconite, sillimanite, bauxite, etc., necessitating complicatedinvesting techniques; (3) relatively low ductilities prohibit anappreciable manipulation of delicate clasps, etc., due to thepossibility of breakage.

My extensive independent research program has been designed to developthoroughly, by the most modern and extensive metallurgical means, analloy to meet the needs of a more modern simplified prostheticdentistry.- Sixty different 9 alloys were investigated in my researchprogram that led to the development of the herein claimed invention.

Specifically, the advantages of my alloy are: (1) the low melting pointpermits the use of gas-air furnaces, platinum wound resistor typefurnaces, etc. to melt the alloy in the dental laboratory; (2) thenobility or high corrosion resistance of the alloy insures that thealloy will not stain in the human mouth; (3) the unique resistance ofthe alloy to attack by sulphur permits the use of plaster of Paris typeinvestments; (4) the relatively high ductility of certain grades of thealloy permits mechanical adjustments of clasps, and the like; (5) thelow melting point, and resistance to attack by sulphur of the alloysimplifies the equipment required in the dental laboratory. Thissimplification of equipment results in a lower first cost of equipment,a lower operating cost, and the elimination of cumbersome and spaceconsuming apparatus; (6) the pleasing, warm, platinum-like color of thealloy is attractive to both patient and dentist.

The invention may be embodied in other specific forms without departingfrom the essential characteristics thereof. Hence, the presentembodiments are therefore to be considered in all respects merely asbeing illustrative and not as being restrictive, the scope of theinvention being indicated by the appended claim rather than by theforegoing description, and all modifications and variations as fallwithin the meaning and purview and range of equivalency of the appendedclaim are therefore intended to be embraced therein.

What it is desired to claim and secure by Letters Patent of the UnitedStates is:

A casting alloy for dentures consisting of, between 0.05% and 0.15%carbon, between 0.70% and 0.90% manganese, between 1.20% and 1.60%silicon, between 17.5% and 19.5% chromium, between 9.0% and 10.0%tungsten, between 29.0% and 31.0% nickel, between 23.0% and 25.0%cobalt, between 0.6% and 0.7% tantalum, between 10.0% and 12.0% copper,between 0.8% and 1.0% aluminum, and a balance of iron.

SIDNEY LOW.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,115,238 Parr Oct. 2'7, 1914 1,115,239 Parr Oct. 27, 19142,309,1 6 Neirman Jan. 26, 1943 2,509,800 Forbes May 30, 1950 2,509,801Blackwood May 30, 1950 FOREIGN PATENTS Number Country Date 604,201Germany Oct. 16, 1934

